1. Field of the Invention
The present invention relates to an apparatus and method for controlling an access means for accessing a recording medium containing at least one area so that the access means accesses at least one area. The present invention also relates to an access apparatus comprising an access means for accessing a recording medium containing at least one area and a control means for controlling the access means. The present invention also relates to an access method, a program, and a write-once recording medium containing a plurality of areas.
2. Description of the Related Art
Optical discs are information recording media having a sector structure. Recently, AV data such as audio and video data has been digitized, and therefore, there is a demand for higher density and larger capacity optical discs.
As an optical disc which realizes large capacity, BD (Blu-ray Disc) has been being developed. A type of BD is a single layer disc capable of holding up to 25 gigabytes (GB) of data, which is 5 times or more larger than that of DVD. The recording speed is also increased to about three times higher than that of DVD. Recording/reproduction of a high-density disc, such as a BD, requires high-precision servo control or signal processing. To achieve this, functions for adjusting various reproduction control parameters are required when starting up a disc after the disc is loaded.
A reproduction control parameter is, for example, a focus position at which a light spot converges on an optical disc. The focus position is adjusted by, for example, a method for minimizing jitter which indicates the quality of a reproduction signal (Japanese Laid-Open Publication No. 10-149550).
Hereinafter, apparatus startup and focus position adjustment will be described.
FIG. 16 shows an exemplary startup procedure for a conventional apparatus. Hereinafter, a startup procedure for a conventional apparatus will be described step by step with reference to FIG. 16.
Step S1201: a laser of a reproduction apparatus emits light. An optical disc is irradiated with a light beam having a reproduction power.
Step S1202: a disc motor is activated. The optical disc is rotated with a predetermined speed.
Step S1203: a control (focusing control) is started so as to control an objective lens for controlling a laser beam to focus on the optical disc.
Step S1204: a control (tracking control) is started so as to move and cause the focus position to follow a spiral track.
Step S1205: a reproduction pickup is shifted to a prerecorded area previously determined on the optical disc.
Step S1206: the focus over the optical disc is moved little by little from the optical pickup toward the optical disc, while measuring jitter recorded in the prerecorded area. In other words, in step S1206, a focus position which provides the most satisfactory reproduction quality is determined while repeating reproduction of the prerecorded area.
As used herein, jitter is an indicator for indicating the quality of a reproduction signal. Jitter indicates a deviation of a reproduction signal in a time-axis direction.
Step S1207: as in Step S1206, jitter of the prerecorded area is measured while tilting the lens of the pickup little by little. In Step S1207, the tilt of the lens is set to a value which minimizes a jitter value (i.e., satisfactory signal quality).
As described above, the apparatus is adjusted by, for example, measuring jitter in the prerecorded area so that the reproduction signal quality becomes most satisfactory.
FIG. 17 is a diagram for explaining an exemplary focus position adjusting method. The horizontal axis indicates a focus offset (focus position) to be set, where the focus position is shifted farther from the lens as the offset value is increased. The vertical axis indicates a jitter value.
In general, a relationship between a focus position and jitter is such that a jitter value is minimized at the best focus position, and is increased when the focus is deviated from the best focus position (see FIG. 17).
The exemplary focus position adjusting method is performed as follows. A jitter value is measured while a focus offset value is increased little by little from a small value. A focus offset is determined when the jitter value is minimized. The focus offset value is set to a and a jitter value is measured in the prerecorded area to obtain a jitter value J(a). Similarly, the focus offset value is set to b, c or d, and thereafter, a jitter value J(b), J(c) or J(d) is respectively measured. In the method, the smallest jitter value is obtained when the focus offset value is c. Thus, the focus offset value is set to c.
As described above, measurement of an indicator (e.g., jitter, etc.) is essential for accurate adjustment of a reproduction control parameter, such as a focus position or the like. Therefore, the presence of a recorded area, in which an indicator can be measured, is essentially required for learning.
Conventionally, reproduction-only discs are shipped after data has been recorded thereinto. Therefore, it is easy to detect a recorded area. Also, in DVD-RAM (Digital Versatile Disc Random Access Memory) and DVD-RW (Digital Versatile Disc Rewritable), a control information area which is necessarily recorded before shipment is included in a lead-in area at an inner peripheral portion of the disc, and the control information area is used to adjust a reproduction control parameter.
However, in some types of rewritable or write-once optical discs (e.g., BD), control information is recorded in the form of wobble of a track at an inner peripheral portion of the optical disc (wobble recording method). Therefore, such optical discs do not necessarily have a recorded area which can be used to measure a reproduction quality indicator (e.g., jitter, etc.). As a result, it is difficult to perform adjustment based on a reproduction quality indicator for an optical disc which has no recorded area.
Further, in order to achieve a high-speed startup using a recorded area, it is necessary to efficiently determine whether or not an optical disc has a recorded area.
Further, in order to efficiently determine whether or not an optical disc has a recorded area while various reproduction control parameters are not sufficiently adjusted, reliability is required for determination of whether data is recorded or unrecorded in an area.
Further, in multi-layer recording media having a plurality of recording layers, reproduction control parameters need to be adjusted appropriately for the recording layers having different characteristics.
Further, a recorded area needs to be searched for efficiently in each of a rewritable optical disc and a write-once optical disc which have different sequences of recorded data.
Further, when a search for a recorded area is not performed in an optical disc which has no recorded area, it is determined that an optical disc has no recorded area in the next reproduction control parameter adjustment.
Further, in write-once optical discs, data can be written only once. Therefore, a limited area needs to be used effectively.